13 Cathodic Protection

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13 Cathodic Protection

  1. 1. Organisation Chart Jotun Cathodic Protection Jotun Cathodic Protection Jotun Decorative ( Scandinavia) Jotun Protective Coatings Jotun Decorative Paints Jotun Marine Coatings Jotun Paints Jotun Powder Coatings Jotun Group
  2. 2. Corrosion of a metal or alloy <ul><li>Corrosion is a reaction between the metal and the surrounding environment </li></ul><ul><li>The corrosion rate depends on the properties of the metal and the corrosivity of the environment. </li></ul><ul><li>Corrosion is dissolution of the metal, among other things involving the release of electrons: </li></ul><ul><li> Fe Fe + 2e </li></ul>2+
  3. 3. What is cathodic protection ? <ul><li>Cathodic protection (CP) is a method for reducing the corrosion rate of a metal. </li></ul><ul><li>The principle is based on “Supplying electrons to the base material”. </li></ul><ul><li>This is done by either: </li></ul><ul><ul><li>Connecting the structure to a more electro- negative material (Sacrificial anode) </li></ul></ul><ul><ul><li>Connecting the structure to an external electron source (Impressed current) </li></ul></ul>
  4. 4. How to protect a structure <ul><li>Corrosion Protection can be achieved by : </li></ul><ul><li>Sacrificial Anode Cathodic Protection System </li></ul><ul><li>Impressed Current Cathodic Protection System </li></ul><ul><li>Both systems supply electrons to the structure. </li></ul><ul><li>The structure will become more negative and metal dissolution will be prevented </li></ul>
  5. 5. Type of Products <ul><li>Sacrificial anodes </li></ul><ul><li>Electrolytic descaling </li></ul><ul><li>Impressed Current Cathodic Protection Systems (ICCP) </li></ul><ul><li>Electrolytic Antifouling </li></ul>
  6. 6. <ul><li>Zinc </li></ul><ul><ul><li>Noranode </li></ul></ul><ul><ul><li>Coral Z </li></ul></ul><ul><li>Aluminium </li></ul><ul><ul><li>Coral A </li></ul></ul><ul><ul><li>Coral A high grade </li></ul></ul><ul><li>Magnesium </li></ul>Type of Sacrificial Anodes
  7. 7. Type of Products <ul><li>Cathodic protection engineering and design </li></ul><ul><li>Sacrificial anodes </li></ul><ul><li>Impressed current systems </li></ul><ul><li>Electrolytic Antifouling Systems </li></ul><ul><li>Magnesium strips (Electrolytic descaling) </li></ul><ul><li>Grounding equipment </li></ul>
  8. 8. Type of Services <ul><li>Surveying, inspection and reporting </li></ul><ul><li>Cathodic protection engineering and design </li></ul><ul><li>Potential measurements </li></ul><ul><li>Servicing and Log sheet evaluation </li></ul><ul><li>Technical support and advice </li></ul>
  9. 9. Type of Products and Services <ul><li>Cathodic protection engineering and design </li></ul><ul><li>Servicing, inspection and reporting </li></ul><ul><li>Sacrifical anodes </li></ul><ul><li>Magnesium strips (Electrolytic descaling) </li></ul><ul><li>Impressed Current Cathodic Protection Systems </li></ul><ul><li>Electrolytic Antifouling System </li></ul><ul><li>Log sheet evaluation </li></ul><ul><li>Grounding equipment </li></ul>
  10. 10. <ul><li>Impressed Current Cathodic Protection Systems </li></ul><ul><li>Transformer rectifiers </li></ul><ul><li>Impressed current anodes </li></ul><ul><li>Reference electrodes </li></ul><ul><li>Monitoring equipment </li></ul><ul><li>Shaft grounding equipment </li></ul><ul><li>Rudder grounding </li></ul>Type of Products
  11. 11. Type of products <ul><li>Grounding equipment </li></ul><ul><li>Rudder grounding </li></ul><ul><li>Shaft grounding equipment </li></ul><ul><li>Earthing cables </li></ul>
  12. 12. Type of Products <ul><li>Magnesium Strips for descaling </li></ul><ul><li>Magnesium strips </li></ul><ul><li>Clamps </li></ul>
  13. 13. For Norway Objects to be Protected: <ul><li>Ships </li></ul><ul><li>Offshore platforms and rigs </li></ul><ul><li>Subsea installations </li></ul><ul><li>Subsea pipelines </li></ul><ul><li>Harbour facilities </li></ul><ul><li>Storage tanks </li></ul><ul><li>Buried tanks and pipelines (onshore) </li></ul>
  14. 14. Objects to be Protected: <ul><li>Ships </li></ul><ul><li>Offshore platforms and rigs </li></ul><ul><li>Subsea installations </li></ul><ul><li>Subsea pipelines </li></ul><ul><li>Harbour facilities (Sacrificial anodes) </li></ul>
  15. 15. Marine Objects to be Protected: <ul><li>Ships </li></ul><ul><li>FPSO / FSU </li></ul><ul><li>Mobile rigs </li></ul><ul><li>Floating dry-docks </li></ul><ul><li>Barges </li></ul>
  16. 16. Norwegian Sector. Offshore and Industry Objects to be Protected : <ul><li>Offshore platforms </li></ul><ul><ul><li>Fixed / floating </li></ul></ul><ul><ul><li>Concrete / steel </li></ul></ul><ul><li>Subsea installations </li></ul><ul><ul><li>(templates/manifolds/ modules) </li></ul></ul><ul><li>Subsea pipelines </li></ul><ul><li>Harbour facilities </li></ul><ul><ul><li>Piles </li></ul></ul><ul><ul><li>Sheet piles </li></ul></ul><ul><li>Buried tanks and pipelines (onshore) </li></ul><ul><li>Storage tanks </li></ul>
  17. 17. Offshore and Industry Objects to be Protected: <ul><li>Offshore platforms </li></ul><ul><ul><li>Fixed / floating </li></ul></ul><ul><ul><li>Concrete / steel </li></ul></ul><ul><li>Subsea installations </li></ul><ul><ul><li>(templates/manifolds/ modules) </li></ul></ul><ul><li>Subsea pipelines </li></ul><ul><li>Harbour facilities </li></ul><ul><ul><li>Piles </li></ul></ul><ul><ul><li>Sheet piles </li></ul></ul>
  18. 18. <ul><li>Iron (steel) in its natural state exist primarily as iron ore </li></ul><ul><li>Energy added at melting and refining are released by the corrosion process </li></ul><ul><li>Coatings reduce corrosion rate </li></ul><ul><li>Cathodic protection supply energy to stop corrosion </li></ul>Energy Corrosion and corrosion protection Time E 1 E 2 Iron ore Refining Rust = Iron ore Corrosion Pure metal or an Alloy Cathodic protection Energy offered by Cathodic protection Coating reduces corrosion rate
  19. 19. Freely Corroding Steel Cathode 2 e - Anode Cathode Sea water (electrolyte) 2 e - 2 e - 2 e - Steel plate - Fe 2+ ½ O 2 + H 2 O + 2e  2OH - ½ O 2 + H 2 O + 2e  2OH - -
  20. 20. Potential, mV vs. Cu/CuSO 4 Zn -580 +500 Freely corroding steel -700 -800 +250 Mixed potential ( Protection potential) -900 -1000 -1080 0 Freely corroding Zinc The Principle of Cathodic Protection Potentials vs. different Reference Electrodes
  21. 21. Cathodic Protection Steel protected by a Sacrificial anode A calcareous deposit is formed on the steel surface 2 e Steel Zinc Zn = Zn + 2 e O 2 2+ - - ½ O 2 + H 2 O + 2e  2OH - -
  22. 22. Steel Current Source Current O 2 2 e- Permanent anode Cathodic protection Impressed current system A calcareous deposit is formed on the steel surface Reaction at the cathode ½ O 2 + H 2 O + 2e  2OH - - Reaction at the anode 2 Cl  ½ Cl 2 + 2e H 2 O  2H + ½ O + 2e - - - +
  23. 23. Rapid corrosion General corrosion Some corrosion 100% Cathodic protection Overprotection Possible coating damage Corrosion Potentials in Seawater Zinc, Ag/Ag Cl and Cu/CuSO 4 R eference Electrodes Increasing polarisation Ag / Ag Cl Zinc + 0.50 - 0.25 + 0.0 + 0.25 - 0.55 - 1.30 -1.05 - 0.80 Potentials in volt - 0.60 - 1.35 -1.10 - 0.85 Cu / CuSO 4
  24. 24. Full cathodic protection (Steel surface passivated) Free corrosion of steel Corrosion reduction , % vs Zn 450 400 350 300 250 mV vs Ag/AgC1 -600 -650 -700 -750 -800 mV Reduction of corrosion rate of steel by cathodic protection. Moving seawater Negative polarisation, mV 0 50 87,5 0 50 100 150 200 Actual potential of the steel
  25. 25. Marine Necessary Information to do a CP Design <ul><li>Type of structure </li></ul><ul><li>Design lifetime </li></ul><ul><li>Coating system and condition </li></ul><ul><li>Trade </li></ul><ul><li>Surface area to be protected </li></ul><ul><ul><li>Drawings </li></ul></ul><ul><ul><li>Tank capacity plan </li></ul></ul><ul><li>Ballasting period. </li></ul><ul><li>Class / Safety restrictions </li></ul>
  26. 26. Marine Design Criteria <ul><li>Design lifetime </li></ul><ul><li>Coating system and condition </li></ul><ul><li>Current density (Coating type and damages) </li></ul><ul><li>Current distribution </li></ul><ul><li>Electrolytic resistivity </li></ul><ul><li>Environmental conditions / impacts </li></ul><ul><li>Ballasting period. </li></ul>
  27. 27. Protective Design criteria <ul><li>Type of structure </li></ul><ul><li>Surface area to be protected </li></ul><ul><li>Design lifetime </li></ul><ul><li>Coating system and condition </li></ul><ul><li>Protection potential </li></ul><ul><li>Anode capacity </li></ul><ul><li>Current distribution </li></ul><ul><li>Electrolyte resistivity </li></ul><ul><li>Environmental conditions / impacts </li></ul><ul><li>Safety restrictions </li></ul>
  28. 28. Current Density Requirement Depends On: <ul><li>A. Environmental parameters </li></ul><ul><li>Sea water composition and salinity </li></ul><ul><li>Sea water temperature </li></ul><ul><li>Specific resistivity of sea water </li></ul><ul><li>Sea water velocity </li></ul><ul><li>Other factors, marine growth </li></ul><ul><li>B. Steel surface </li></ul><ul><li>Painted / not painted </li></ul><ul><li>Steel temperature </li></ul><ul><li>Coating system, if any </li></ul><ul><li>Condition of coating system </li></ul>
  29. 29. Sacrificial Anode material selection <ul><li>Main Types </li></ul><ul><li>Zinc </li></ul><ul><li>Aluminium </li></ul><ul><li>Magnesium </li></ul><ul><li>Anode material selection </li></ul><ul><li>Chemical composition </li></ul><ul><li>Electrochemical performance </li></ul><ul><li>- Anode potential </li></ul><ul><li>- Stable current </li></ul><ul><li>- Consumption </li></ul><ul><li>Anode corrosion pattern </li></ul><ul><li>Price </li></ul><ul><li>Class requirements </li></ul>
  30. 30. Initial/final design current densities in A/m 2 Tropical (> 20 o C) Sub-Tropical (12-20 o C) Temperate (7 - 12 o C) Arctic (< 7 o C) 0.150 0.090 0.170 0.110 0.200 0.130 0.250 0.170 0.130 0.080 0.150 0.090 0.180 0.110 0.220 0.130 Depth (m) 0 - 30 > 30 Current density requirement acc. to DNV RP B401 (1993)
  31. 31. Me4an (average) design current densities in A/m 2 0 - 30 > 30 0.070 0.080 0.100 0.120 1) 0.060 0.070 0.080 0.100 1) Effect of any ice scouring are not included Current density requirement acc. to DNV RP B401 (1993) Tropical (> 20 o C) Sub-Tropical (12-20 o C) Temperate (7 - 12 o C) Arctic (< 7 o C) Depth ( m)
  32. 32. Coating Categories Acc. to DNV RP B401 (1993) <ul><li>Category I: </li></ul><ul><li>One layer of primer coat, about 50 microns nominal DFT (Dry Film Thickness) </li></ul><ul><li>Category II: </li></ul><ul><li>One layer of primer coat, plus minimum one layer of intermediate top coat, 150 to 250 microns nominal DFT. </li></ul>Category III: One layer of primer coat, plus minimum two layers of intermediate/top coats, minimum 300 microns nominal DFT Category IV: One layer of primer coat, plus minimum three layers of intermediate top coats, minimum 450 microns nominal DFT.
  33. 33. Coating Category Depth (m) I II III IV k 1 = 0.10 k 2 0 - 30 0.10 0.03 0.015 0.012 > 30 0.05 0.02 0.012 0.012 k 1 = 0.05 k 2 k 1 = 0.02 k 2 k 1 = 0.02 k 2 where fc = coating break down factor t = coating lifetime k 1 and k 2 = constants dependent on coating properties f c = k 1 + k 2 t Coating Break Down Factor Acc. to DNV RP B401 (1993)
  34. 34. Protective Design Sacrificial Anode System <ul><li>A. Design criteria </li></ul><ul><li>Current density requirement </li></ul><ul><ul><li>initial </li></ul></ul><ul><ul><li>mean </li></ul></ul><ul><ul><li>final </li></ul></ul><ul><li>Design lifetime </li></ul><ul><li>Anode material </li></ul><ul><li>B. Net anode weight requirement </li></ul><ul><li>W= Exposed surface area (m²) </li></ul><ul><li>i = Mean current density (A/ m²) </li></ul><ul><li>C= Anode concumption rate (11.2 kg/year for Zn) </li></ul><ul><li> ( 3.39 kg/year for Al) </li></ul><ul><li>L = Design lifetime </li></ul><ul><li>U = Utility factor (0.90, normally) </li></ul><ul><li>C. Initial and final current requirement </li></ul><ul><li>I INITIAL = A * i init </li></ul><ul><li>I FINAL = A * i final </li></ul><ul><li>D. Anode current system capacity </li></ul><ul><li>Anode design (shape and size) </li></ul><ul><li>Number of anodes </li></ul>
  35. 35. Jotun Anode Alloys <ul><li>Coral A </li></ul><ul><li>Al-Zn-In Alloy </li></ul><ul><li>Increased consumption rate by increasing temperature </li></ul><ul><li>Coral Z </li></ul><ul><li>Zn alloy according to U.S. Mil. Spec. A-18001 </li></ul><ul><li>Intergranular corrosion above approximately 45 ºC </li></ul><ul><li>Noranode </li></ul><ul><li>Zn-Al-Mg Alloy </li></ul><ul><li>Environmental friendly </li></ul><ul><li>Mil. Spec properties below 25 ºC </li></ul><ul><li>Cost effective at elevated </li></ul><ul><li>temperature. </li></ul><ul><ul><li>Reduced intergranular corrosion </li></ul></ul><ul><ul><li>Current capacity and consumption </li></ul></ul><ul><ul><li>rate relatively stable at increasing </li></ul></ul><ul><ul><li>temperatures </li></ul></ul><ul><ul><li>Recommended above 50 ºC </li></ul></ul>
  36. 36. Comparison of Cathodic Protection Systems General Advantages : <ul><li>Sacrificial anode systems </li></ul><ul><li>Simple, reliable and free from in-service operator surveillance </li></ul><ul><li>System installation is simple </li></ul><ul><li>Impressed current systems </li></ul><ul><li>Flexibility under widely varying operating conditions </li></ul><ul><li>Weight advantage for large capacity, long life systems (reduced sea water drag) </li></ul><ul><li>Low life cycle cost (LCC) </li></ul><ul><li>Low installation cost </li></ul><ul><li>for short term protection </li></ul>
  37. 37. Comparison of Cathodic Protection Systems General Disadvantages : <ul><li>Sacrificial anode systems </li></ul><ul><li>Large weight for large capacity, long life systems. </li></ul><ul><li>Response to varying operating conditions is limited. </li></ul><ul><li>Hydrodynamic loadings can be high (Seawater drag) </li></ul><ul><li>Impressed current systems </li></ul><ul><li>Relative complexity of system demands high level of design expertise. </li></ul><ul><li>In-service operator surveillance required. </li></ul><ul><li>Vulnerable to component failure or loss of power. </li></ul>
  38. 38. Why Choose an ICCP System on Hull <ul><li>Smooth hull, no drag </li></ul><ul><li>Flexible dry-docking intervals </li></ul><ul><li>Low cost for long term operation </li></ul><ul><li>Long lifetime, minimum of maintenance </li></ul><ul><li>No welding required at dry docking </li></ul><ul><li>No risk of damaging internal Paint systems </li></ul><ul><li>Fully automatic corrosion protection </li></ul>
  39. 39. Why Choose a SACP System on Hull <ul><li>Simple installation </li></ul><ul><li>Maintenance free between dry docking </li></ul><ul><li>Low cost for short term operation </li></ul><ul><li>World-wide availability </li></ul>
  40. 40. Lifecycle Cost of CP Systems 13000 DWT Car Carrier 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 USD ICCP Al Zn 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Years Indicates Dry-docking Replacement of an ICCP component Anodes and Reference electrodes can be replaced whilst in service. Normally, this is carried out at the dry-docking
  41. 41. Life Cycle Cost of CP Systems Panamax Bulkcarrier 0 20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000 USD ICCP Al Zn 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Years Indicates Dry-docking Replacement of an ICCP component Anodes and Reference electrodes can be replaced whilst in service. Normally, this is carried out at the dry-docking
  42. 42. Cathodic Protection of Ballast Water Tanks <ul><li>1. Impressed current systems are not practical, and in most Classification Societies not permitted. </li></ul><ul><li>2. Magnesium anodes are not permitted. </li></ul><ul><li>3. In cargo, or adjacent tanks where the flash point is below 60 deg. C, Aluminium anodes are only permitted where the kinetic energy can not exceed 27,5 kpm (275 J). </li></ul><ul><li>4. There are no restrictions on the positioning of Zinc anodes. </li></ul>
  43. 43. Tanks: Lloyd's register DNV Segregated ballast 108 100 - 110 Dirty ballast 86 40 - 60 Washed cargo 108 80 - 90 Top wing 120 120 Coated (epoxy) 5 5 - 10 Soft Coats 20 - 40 Current density criteria mA/m 2 Current density Design Criteria
  44. 44. Example: Tanker vessel. Clean ballast water. Upper wing tank <ul><li>Anode information </li></ul><ul><li>Anode type : ZTL - 230 </li></ul><ul><li>Gross weight : 23 kgs </li></ul><ul><li>Net weight : 21,2 kgs </li></ul><ul><li>Current output : 1,3 Amps </li></ul><ul><li>Input from customer </li></ul><ul><li>Area : 6400 m 2 </li></ul><ul><li>Current density : 120 mA/m 2 </li></ul><ul><li>Life time : 4 years </li></ul><ul><li>Ballast time : 50 % </li></ul><ul><li>Paint system : Unpainted </li></ul>
  45. 45. Tanks Conversion Factors from Volume to Area C.T : W.T : Forepeak : D.B.T : U.W.T : Volume * 0.7 - 0.9 Volume * 1.5 - 2.5 Volume * 1,5 - 2.5 Volume * 0.5 - 0.6 Volume * 1.5 - 2.5 = Area m² = Area m² = Area m² = Area m² = Area m² Examples: Deck head is included Exact calculations must be based on drawings
  46. 46. Net weight: 6400 m 2 x 120 mA/m 2 x 4 yrs x 50% x 11,2 kg/A.yr ------------------------------------------------------ = 17203 kg 1000 100 17203 kg. No. of anodes : --------------- = 812 pcs : 812 pcs ZTL-230 21,2 kg/pc Gross weight : 812 kg x 23kg/pcs = 18676 kg Check of current requirement: 6400 m 2 x 0,12 A/m 2 = 768 Amp Total current output : 1,3 Amp/pc x 812 pcs = 1055,6 Amp Example: Tanker vessel. Clean Ballast Water. Upper wing tank
  47. 47. <ul><li>Information required: </li></ul><ul><li>Theoretical calculation of net weight of anodes </li></ul><ul><ul><li>From previous calculation </li></ul></ul><ul><li>Number of small compartments </li></ul>Design of Sacrificial Anode System Double Bottom and Other Narrow Tanks
  48. 48. <ul><li>Calculation: </li></ul><ul><li>Anode net weight: </li></ul><ul><li>Total net weight, kg = Net weight/pc </li></ul><ul><li>NOTE: </li></ul><ul><li>Usually, the number of compartments equal the number of pieces: Require one anode per compartment </li></ul><ul><li>Use nearest standard anode type </li></ul>Design of Sacrificial Anode System Double Bottom and Other Narrow Tanks Number of compartments (pc)
  49. 49. Example: Tanker vessel. Clean ballast water. Double Bottom Tank <ul><li>Anode information </li></ul><ul><li>Anode type : ZTL - 230 </li></ul><ul><li>Gross weight : 23 kgs </li></ul><ul><li>Net weight : 21,2 kgs </li></ul><ul><li>Current output : 1,3 Amps </li></ul><ul><li>Input from customer </li></ul><ul><li>Area : 6400 m 2 </li></ul><ul><li>Current density : 120 mA/m 2 </li></ul><ul><li>Life time : 4 years </li></ul><ul><li>Ballast time : 50 % </li></ul><ul><li>Paint system : Unpainted </li></ul>
  50. 50. Net weight: 6400 m 2 x 120 mA/m 2 x 4 yrs x 50% x 11,2 kg/A.yr ------------------------------------------------------ = 17203 kg 1000 100 17203 kg. No. of anodes : --------------- = 812 pcs : 812 pcs ZTL-230 21,2 kg/pc Gross weight : 812 kg x 23kg/pcs = 18676 kg Check of current requirement: 6400 m 2 x 0,12 A/m 2 = 768 Amp Total current output : 1,3 Amp/pc x 812 pcs = 1055,6 Amp Example: Tanker vessel. Clean Ballast Water. Double Bottom Tank
  51. 51. ICCP - Log report Readings Current Output Development With Time 100 - 80 - 60 - 40 - 20 - | | | | | | 1 2 3 4 5 6 System capacity Amp. Years 1. docking 2.. docking 3. docking Grounding (Loss of coating) Example
  52. 52. Cathodic protection of tanks Current density at different coating breakdown ratio Current density mA/m² 70 60 50 40 30 20 10 2 80 90 Tar Epoxy Epoxy Mastic Upper Wing tank 0 5 10 20 30 40 50 60 70 80 90 100 110 120 100 Cargo/dirty ballast tanks Clean ballast tanks fore-and aft. peak tanks Cargo/clean ballast tank slower wing/double bottom Soft coat / Flow coat Coating breakdown
  53. 53. Ship hull: Current Density at Different Paint Damage Current density, mA/ m² Paint damage, % 100 45 15 0 20 70 Not applicable: Repaint ICCP is recommended, not sacrificial anodes Sacrificial Anodes and ICCP can be used
  54. 54. *) Potential in seawater measured versus a copper/coppersulphate reference electrode Galvanic Series in Sea Water Corrosion Potentials vs. 3 Reference Electrodes Graphite + 0.25 + 1.28 + 0.17 Titanium 0 + 1.03 - 0.08 Stainless steel (Passive) - 0.50 + 0.98 - 0.13 Copper-Nickel (90/10) - 0.23 + 0.80 - 0.31 Copper - 0.33 + 0.70 - 0.41 Brass - 0.34 + 0.69 - 0.42 Stainless steel (Corroding) - 0.35 + 0.68 - 0.43 Mild steel - 0.66 + 0.37 - 0.69 Aluminium - 0.80 + 0.23 - 0.88 Zinc - 1.03 0 - 1.11 Magnesium - 1.60 - 0.57 - 1.68 Metal / Alloy Ag / AgCl Zn Cu/Cu SO 4
  55. 55. Corrosion Secondary structure Pipeline Anode +_ Interference
  56. 56. 2 Type Anode current density in seawater ( A/m ) Consumption rate ( kg/A year) 500 - 1000 < 1 x 10 500 - 1000 1000 - 5000 6 x 10 1 x 10 160 - 220 160 - 220 0,05 - 0,2 0,03 - 0,06 10 - 40 0,2 - 0,5 10 - 40 0,2 - 0,5 - 7 - 9 -6 -6 -5 2 MIXED METALOXYDE PLATINIUM - Disc - Thread LEAD-SILVER Pb - 6% Sb - 1% Ag Pb - 6% Sb - 1% Ag GRAPHITE IRON-SILISIUM Fe - 14,5% Si - 4,5% Cr SCRAP IRON Impressed current system anodes
  57. 57. Anode performance data Anode Specific Closed circuit Driving Capacity Consumption types gravity potential vs. Zn voltage (Ah/Kg) rate (Kg/dm ) ( Volt) (Volt) ( Kg/ A*Year) 3 Zinc Aluminium Magnesium 7.13 0 0.23 781 11.2 2.78 -0.02 0.25 2585 3.39 1.84 -0.47 0.7 1200 7.3
  58. 58. Aluminium Anodes Small vessels This guide is based on a 3 year (36 month) replacement period (dry-docking interval). Vessel Type Surface Anode Type Current Density - mA/m 2 Number of Total Area (% coating breakdown) Anodes Weight Kgs Tug / Small Vessels 500 A - 50 25 (15 %) 32 160 Supply Vessel 2000 A - 80 20 (10 - 15 %) 60 480 Reefer / Container 4000 A -130 15 (5 - 10 %) 58 754 Tanker / Bulker 18000 A - 180 10 (2-5 %) 120 2160 This design is for the hull only and does not allow for the seachests, thruster tunnels etc.. The calculation is the same, but with specific current densities.
  59. 59. This guide is based on a 3 year (36 month) replacement period (dry-docking interval). Vessel Type Surface Area Anode Type Current Density Number of pieces Total - mA/m 2 Gross (% coating breakdown) Weight - Kgs Tug / Small Vessels 500 Z-85 25 (15 %) 54 459 Supply Vessel 2000 Z-160 20 (10 - 15 %) 92 1472 Reefer / Container 4000 Z-270 15 (5 - 10 %) 80 2160 Tanker / Bulker 18000 Z-200 10 (2-5 %) 316 6320 This design is for the hull only and does not allow for the seachests, thruster tunnels etc.. The calculation is the same, but with specific current Densities Zinc Anodes
  60. 60. Principle : Effect of using CP Corrosion Curves depend on - Coating condition - CP-design Coating breakdown CP installed CP and coating at newbuilding Time Corrosion
  61. 61. Steel passivation by sacrificial anodes Paint Steel Rust Without Cathodic Protection Paint Steel With Cathodic Protection Anode Anode current Seawater Seawater Calcareous layer
  62. 62. Ships hull: Current density as function of coating breakdown <ul><li>Coating breakdown Current density </li></ul><ul><li>2 - 5 % 10 mA/m 2 </li></ul><ul><li>5-10 % 15 mA/m 2 </li></ul><ul><li>10-15 % 20 mA/m 2 </li></ul><ul><li>15-20 % 30 mA/m 2 </li></ul><ul><li> 20-25 % 40 mA/m 2 </li></ul><ul><li> 25-30 % 50 mA/m 2 </li></ul>
  63. 63. Location Current density Seachests Thruster tunnel Propeller nozzle Rudder Rudder flaps Anti-suction tunnels Propeller (Uncoated) Azimuth propeller 40 mA/m 2 150 mA/m 2 150 mA/m 2 100 mA/m 2 150 mA/m 2 100 mA/m 2 500 mA/m 2 150 mA/m 2 CP of ships: Additional Areas Requiring Protection.
  64. 64. Sacrificial Anode System <ul><li>Aluminium alloy anodes </li></ul><ul><li>Zinc alloy anodes (technically equal) </li></ul><ul><li>Aluminium is recommended prior to zinc because: </li></ul><ul><li>Aluminium anode weight is approx. 1/3 of zinc </li></ul><ul><li>Total price for equal protection: Al. anodes approx 1/2 of Zinc anodes </li></ul><ul><li>Lower installation costs due to weight difference </li></ul>
  65. 65. Cathodic Protection <ul><li>ICCP - Impressed Current </li></ul><ul><li>SACP - Sacrificial Anodes </li></ul><ul><li>EAF - Electrolytic Antifouling System for seawater systems (CUPROBAN) </li></ul><ul><li>Slip ring arrangement for propeller shaft </li></ul><ul><li>Coatings and Cathodic Protection </li></ul><ul><li>The Single Source Solution </li></ul>
  66. 66. Sacrificial Anode System Disadvantages <ul><li>Increases the frictional resistance </li></ul><ul><li>Adds weight to the vessel </li></ul><ul><li>The shipyard often supply the anodes at a very low price (charge more for installation) </li></ul>
  67. 67. Cathodic protection Sacrificial Anodes or Impressed Current <ul><li>Anodes increase the frictional resistance compared with impressed current systems </li></ul><ul><li>Adds weight to the vessel </li></ul><ul><li>Aluminium anode weight is approx. 1/3 of zinc </li></ul><ul><li>Total price for equal protection: </li></ul><ul><ul><li>Al. anodes approximately half the price of Zinc anodes </li></ul></ul>
  68. 68. Location of Pitguard Anodes Web Frame Web Frame
  69. 69. Type of products Grounding Equipment <ul><li>Rudder grounding </li></ul><ul><li>Shaft grounding equipment </li></ul><ul><li>Earthing cables </li></ul>
  70. 70. Slipring Arrangement Shaft Silver Graphite Brush Steel Slipring Earth to Hull mV meter Silver Inlay
  71. 71. Slip Ring Arrangement <ul><li>Protects against spark corrosion in the engine bearings </li></ul><ul><ul><li>Very high cost to replace bearing </li></ul></ul><ul><ul><li>The vessel cannot operate with damaged bearings </li></ul></ul><ul><li>Reduces corrosion on propeller </li></ul><ul><ul><li>Extends propeller life </li></ul></ul><ul><ul><li>Reduces polishing needs on the propeller </li></ul></ul>
  72. 72. Slip Ring Arrangement <ul><li>Grounding of the propeller and shaft </li></ul><ul><li>Fixed to intermediate shaft in engine room </li></ul><ul><li>Beneficial if SACP or ICCP systems are used </li></ul>
  73. 73. <ul><li>Thank You ! </li></ul>

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